(a) Field of the Invention
The present invention relates to a novel, liquid-crystalline, wholly aromatic copolyester which exhibits well-balanced characteristics in moldability, heat resistance, solvent resistance, and heat stability, and can by synthesized by using relatively low-priced monomers. More particularly, the present invention relates to a novel, wholly aromatic copolyester the molding temperature and the heat resistance of which can be adjusted in specific ranges so as to make it applicable, in a form of engineering plastic, fiber, film, sheet, etc., to various fields including electrical or electronic parts and car parts.
(b) Description of the Related Art
In recent years, liquid-crystalline, thermotropic polymers, particularly liquid-crystalline, wholly aromatic polyesters have attracted interest as thermoplastic resins having excellent mechanical strength, heat resistance, and chemical resistance, and various kinds of liquid-crystalline, wholly aromatic polyesters have actually been developed. Some examples of the liquid-crystalline, wholly aromatic polyesters thus developed include wholly aromatic polyesters disclosed in Japanese Patent Application Kokai Koho (Laid-open) No. 58-29819, Japanese Patent Application Kohai Koho (Laid-open) No. 58-45224, Japanese Patent Application Kokai Koho (Laid-open) No. 59-30821, U.S. Pat. No. 4,614,791, Japanese Patent Application Kokai Koho (Laid-open) No. 59-78232, Japanese Patent Application Kokoku Koho (Publication) No. 58-40976, Japanese Patent Application Kohyo Koho No. 61-501207, Japanese Patent Application Kokai Koho (Laid-open) No. 64-26631, and Japanese Patent Application Kokai Koho (Laid-open) No. 64-40520.
Among these polyesters, the liquid-crystalline polyesters disclosed in Japanese Patent Application Kokai Koho (Laid-open) No. 59-30821 and U.S. Pat. No. 4,614,791 consist of para-substituted aromatic dicarboxylic acid components and diol components derived from substituted hydroquinones and hydroquinone and are easy to dissolve in solvents. These liquid-crystalline polyesters, however, have a relatively low content of hydroquinone component, thereby causing a problem that molded objects are inferior in heat stability and solvent resistance. The liquid-crystalline polyester disclosed in Japanese Patent Application Kohyo Koho No. 61-501207, which consists of para-substituted aromatic dicarboxylic acid components and diol components derived from specific substituted hydroquinones, have problems that not only does it have a high melting point, but it needs expensive monomers for its preparation.